Wang Aijun is the editor of the Beijing News, one of China's most influential private daily newspapers. Yet here in the capital, Wang said, he often feels like a second-class citizen.

He pays Beijing taxes, but his teenage son is not allowed to attend a Beijing public high school. To install a telephone or an Internet line, he must pay in advance. He is charged more for a ticket to some city parks. He doesn't qualify for a subsidized apartment. He cannot enroll his family in the city's public health-insurance program.

The reason for the discrimination? Despite having lived and worked in Beijing for seven years, Wang still does not have that most sought-after of commodities: a Beijing "hukou."

One of China's oldest tools of population control, the hukou is essentially a household registration permit, akin to an internal passport. It contains all of a household's identifying information, such as parents' names, births, deaths, marriages, divorces, moves and colleges attended. Most important, it identifies the city, town or village to which a person belongs.

The hukou dates back at least 2,000 years, when the Han dynasty used it as a way to collect taxes and determine who served in the army. Mao Zedong's Communist regime revived it in 1958 to keep poor rural farmers from flooding into the cities. It remains a key tool for keeping track of people and monitoring those the government considers "troublemakers."

Critics say the hukou system perpetuates China's growing urban-rural divide. Migrant workers flock to the coastal cities to labor in factories and take other manual jobs, sometimes living many years in places such as Beijing, Shanghai and Guangzhou. Because they lack an "urban hukou," they are forever designated "temporary residents" -- unentitled to subsidized public housing, public education beyond elementary school, public medical insurance and government welfare payments.

People who live in a city such as Beijing but do not have a local hukou must travel to their home towns to get a marriage license, apply for a passport or take the national university entrance exam. Parents and students say the last requirement is particularly onerous, especially if a student has to take the exam in a province that uses different textbooks.

Some economists here say the hukou system is outdated and unsuited to a modern economy that requires the free movement of labor. Others call it "China's apartheid," saying it has created a two-tiered system of haves and have-nots in all the major cities.

"You have a large number of rural migrants who already earn most of their income in the cities, who have been in the cities a long time, but do not have hukou-related benefits," said Tao Ran, an economist at Renmin University. "This system is very bad; it's ridiculous."

Life without a hukou

White-collar professionals also find life more difficult if they happen to be born without the right hukou.

Wang, 42, moved to Beijing seven years ago from Zhengzhou, in Henan province, after he became editor of the Beijing News. The paper could not get him a Beijing hukou, but he took the job anyway. "I thought I should do something I was interested in," Wang said. "I also thought China's hukou system would be reformed in six or seven years."

He estimates that nearly a third of Beijing's 22 million-plus people do not have a Beijing hukou -- including, he said, most members of his newspaper staff. Some reports put the number of temporary residents in the capital at 8 million.

"I've gotten used to living in Beijing without a hukou," Wang said. "A hukou is like the air -- you don't think about it normally. But once you need it and don't have it, you get pretty upset." Wang cited the fees he must pay for his 15-year-old son's expensive international school.

Some get desperate, taking a job they don't really want if it offers them a hukou.

Peng Li, 29, graduated with a law degree from a Beijing university in 2008 and was offered work in a company's legal office. But the offer did not include a guaranteed Beijing hukou, so she took a job as an official in a Beijing suburb.

"This job is kind of boring, and the salary is not high," she said. "I regarded it as a springboard to getting a Beijing hukou."

Some young people seeking a spouse on popular Internet sites will state upfront that they prefer a partner who has a Beijing hukou.

"Girl, 26, from North China, 161 cm tall . . . looking for a guy who was born between 1976 and 1983 and wants to marry within three years," says one posting on a popular site by a girl calling herself "imzly." "I hope you . . . have a Beijing hukou (because I don't have one)."

The Beijing hukou is the most prized, if only because it is the hardest to get. One reason is education: The capital has the country's most highly regarded universities, and those schools reserve a large quota of places for Beijing hukou-holders.

Chinese from outside the city can switch to a Beijing hukou by joining the civil service, getting a job with a state-owned company or achieving a high military rank.

Relaxing the rules

In the 1990s, some cities, including Shanghai, Shenzhen and Guangzhou, began allowing people to acquire a local hukou if they bought property in the city or invested a large sum of money. Shanghai further relaxed the rules last year so that professionals who have lived in the city for seven years as tax-paying temporary residents could qualify.

The Beijing government has taken several small steps toward hukou reform over the years. A Beijing pension can now be transferred to another city, for example, and the city's public kindergartens and grade schools were recently opened to all students, regardless of hukou status.

Some critics advocating an overhaul of the hukou system -- or abolishing it altogether -- said changes must be gradual to avoid large-scale disruption. Some have recommended assigning hukous by income or giving priority to those who have paid taxes in a city.

Whatever the pace of change, experts said, the hukou has outlived its usefulness.

"Migration is inevitable," said Tao of Renmin University. "We're proposing the government should just open all the cities."